The invention relates to an exhaust turbine for a turbo-charger with a rotor rotatably supported in a turbine casing having a spiral inlet duct and provided with an annular space around the rotor provided with a guide vane structure.
DE 196 45 388 A1 discloses an exhaust turbine in which a guide vane structure can be moved axially into an annular space between a spiral inlet duct and a rotor. At its free end, the guide vane structure has a cover ring, which covers an annular gap in the turbine casing into which the guide vane structure is disposed in a retracted position of the guide vane structure. However, the cover ring reduces the axial extent of the annular space and forms a flow resistance in the form of a sharp-edged step in the contour of the spiral inlet duct. The step generates turbulence in the flow and thus causes a loss in efficiency.
It is the object of the present invention to improve the flow conditions in the region of the guide vane structure of the exhaust turbine.
In an exhaust turbine for a turbocharger having a rotor rotatably supported in a turbine casing wherein the turbine casing has a spiral inlet with an annular space disposed directly around the rotor and an axial cavity extending from the annular space axially into the casing and slideably receiving a guide vane structure so as to be movable between a retracted position in the annular space and an extended position, in which the guide vane structure is disposed in the annular space, the guide vane structure has opposite outer and inner cover rings and the turbine casing has a recess opposite the axial cavity so that in the extended position of the guide vane structure its outer cover ring is fittingly received in the recess while the inner cover ring is disposed at the outer end of the axial cavity providing for a smooth inlet flow duct surface.
With this arrangement, the cover ring presents no resistance to the flow of exhaust gas through the guide vane structure and the exhaust gas is deflected exclusively by the guide vanes. It is advantageous here for the edges of the cover ring walls adjacent the guide vanes to be rounded on the inflow side and to fit the contour of the flow duct in a flush manner.
The invention will become more readily apparent from the following description thereof on the basis of the accompanying drawings which illustrate an exemplary embodiment of the invention.